Those interested in energy and climate policy should subscribe to Climate, Etc., hosted by Judith Curry, the fearless one-woman truth seeker in the polarized climate debate. Professor Curry, who is very well credentialed — and respected by the quiet climatologists, not only the so-called skeptics — is arguably the most important voice in the physical science side of today’s climate debate. Not only is her research at the cutting edge of the unsettled science, she regularly, accurately, and fearlessly reports the latest in the science debates
Professor Curry recently testified before the House Committee on Science, Space and Technology, which held a hearing, “The President’s UN Climate Pledge: Scientifically Justified or a New Tax on Americans?” She then answered follow-up questions, from which the indented answers are drawn. (Note: the bold headings are mine and not questions from the Committee–those can be found in her entire response.)
Temperature Impact of Obama’s CO2 Aspirational Goal
If you believe the climate models, then President Obama’s INDC commitment (total of 80% emissions reduction by 2015), then warming would be reduced by 0.011 degrees Centigrade, a number that was provided to me by Chip Knappenberger of CATO using the MAGICC model with an equilibrium climate sensitivity of 3.0oC http://www.cato.org/blog/002degc-temperature-rise-averted-vital-number-missing-epas-numbers-fact-sheet. If the climate models are indeed running too hot, then the warming would be reduced by an even smaller number.
Temperature Impact w/o U.S. Greenhouse Gas Emissions
Eliminating all U.S. greenhouse gas emissions by 2050 would reduce the warming by 0.014oC (as per the EPA MAGICC model). This is an amount of warming that is much smaller than the uncertainty in even measuring the global average temperature.
Bias from Climate Change Orthodoxy
The censure of scientists disagreeing with the IPCC consensus was particularly acute during the period 2005-2010. As revealed by the Climategate emails, there was a cadre of leading climate scientists that were working to sabotage the reviews of skeptical research papers (and presumably proposals for research funding). Further, scientists challenging climate change orthodoxy are subjected to vitriolic treatment in news articles, op-eds and blogs, damaging the public reputation of these scientists. I have heard from numerous scientists who are sympathetic to my efforts in challenging climate change orthodoxy, but are afraid to speak out or even publish skeptical research since they are fearful of losing their job.
Since 2010, things have improved somewhat especially in Europe; I think this has largely been due to reflections following Climategate and the fact that disagreement about climate change is not as starkly divided along the lines of political parties (i.e. the issue is somewhat less politicized). In the U.S., with President Obama’s recent pronouncements about climate denial and climate deniers (as anyone who does not agree with the consensus) has increased the toxicity of the environment (both academic and public) for scientists that question the IPCC consensus on climate change.
Climate Model Overwarming/Problems
Particularly for the past decade, climate models have been running too hot, predicting more warming than has been observed (refer to the figure on page 6 of my testimony http://www.climate-lab-book.ac.uk/comparing-cmip5-observations/.
The discrepancies between observed surface temperatures and climate model simulations indicates that climate models are not useful for predicting climate on decadal time scales (out to 20 years) or for regional spatial scales. If the so-called warming hiatus continues for another few years, then the observations will be completely outside of the envelope of climate model predictions.
I have argued that climate models are not fit for the purpose of simulating decadal scale and regional climate variability. Climate models are mainly useful for scientific exploration of mechanisms in the climate system. Whether they are at all useful for projections of century scale climate change remains to be seen, but I am doubtful.
For the main climate models used in the CMIP5 simulations for the IPCC AR5, climate sensitivity is an emergent property and not one that is easily tuned. For simpler climate models, such as MAGICC http://www.cgd.ucar.edu/cas/wigley/magicc/, climate sensitivity can be tuned, see http://www.cato.org/blog/002degc-temperature-rise-averted-vital-number-missing-epas-numbers-fact-sheet
Natural Climate Variability/Gaps in Knowledge
Solar impacts on climate (including indirect effects). What are the magnitudes and nature of the range of physical mechanisms?
Nature and mechanisms of multi-decadal and century scale natural internal variability. How do these modes of internal variability interact with external forcing, and to what extent are these modes separable from externally forced climate change?
Deep ocean heat content variations and mechanisms of vertical heat transfer between the surface and deep ocean.
The strength of carbon cycle feedbacks (both land and ocean)
Climate dynamics of clouds: Could changes in cloud distribution or optical properties contribute to the global surface temperature hiatus? How do cloud patterns (and TOA and surface radiative fluxes) change with shifts in in atmospheric circulation and teleconnection regimes (e.g. AO, NAO, PDO)? How do feedbacks between clouds, surface temperature, and atmospheric thermodynamics/circulations interact with global warming and the atmospheric circulation and teleconnection regimes?
Whether the warming since 1950 has been dominated by human causes
How much the planet will warm in the 21st century …
Sensitivity of the climate system to external forcing, including fast thermodynamic feedbacks (water vapor, clouds, lapse rate).
IPCC Climate Sensitivity Trends
Since the IPCC AR4 in 2007, both the upper bound (at the very likely level) and lower bound (at the likely level) to climate sensitivity have been lowered. There is a dichotomy between climate model estimates (higher) and observation based estimates (lower)….
Under the Business As Usual Emissions Scenario (RCP8.5), the IPCC AR5 projects a likely increase of global mean surface temperatures for 2081–2100 relative to 1986–2005 to be 2.6°C to 4.8°C (RCP8.5). The likely confidence implies that there is a 34% chance that the increase could lie outside this range. Personally, I think the IPCC is overconfident in their estimate; I would expect the warming to lie below this range.
Likely Climate Sensitivity
The most recent estimates from observations suggest a transient climate response of 1.05 to 1.45 oC and equilibrium climate sensitivity of 1.2 to 1.8 oC [17-83% range]…
For the past decade, global surface temperatures have been running cooler than the model projections. The lack of recent warming appears to be caused by changes in ocean circulations in the Pacific and Atlantic Oceans, with perhaps some contribution from the sun.
Extreme Weather and Climate Policy
Extreme weather and climate events have always occurred and will continue to occur. Further, sea level has been rising since the last ice age. Even if you believe the climate models and the IPCC assessment and we are successful at eliminating CO2 emissions, we would not expect to notice any significant difference in extreme events at the end of the 21st century. Measures to reduce our vulnerability to weather and climate extremes make sense whether or not humans are influencing climate in any significant way.
Obama Climate ‘Insurance’ Policy?
If we are to view climate mitigation policies as an insurance policy, the cost of the policy needs to be commensurate with the possible damage, and the policy has to actually be effective at shielding the policy holder from losses….
The President’s INDC is not a good insurance policy, as per the above criteria.
The 2oC Warming Threshold
The concern about inaction comes from concern about passing the 2oC ‘danger’ threshold, possibly by mid-century. This concern relies on a very weak assessment that 2oC of warming is actually ‘dangerous’ and that we can believe the climate models (which seem to be running too hot).